This investigation plans to conduct a systematic diagnostic and treatment outcome study of adolescent drug abuse clients, aged 21 years or less, in "drug-free" outpatient treatment programs, inpatient programs, and non-hospital residential programs, with the following specific aims: (1)To develop a new valid and reliable diagnostic instrument ("Adolescent Drug Abuse Diagnosis" (ADAD)) that will be useful for improving client diagnostic services, for evaluation of client treatment needs, for treatment planning, and to enhance the potential for conducting research with adolescent drug abuse clients (Study #1); (2)To develop for distribution to the field an instruction and scoring manual which will enable and facilitate use of the ADAD instrument by clinical and research personnel in programs for adolescent drug abusers (Study #1); (3)To test the usefulness of this new instrument for predicting outcome of outpatient treatment (Study #1), (4)To develop a method for matching adolescent drug abuse clients to three types of treatment environments: outpatient, inpatient, and non-hospital residential according to the profiles of their problems (needs for treatment).